Apparatus and method for collecting solar energy

Abstract

An absorber panel for solar energy is formed of two sheets with spacer means extending therebetween to maintain a spaced relationship between the sheets and provide a flow passage for a heat exchange liquid such as water. A pressure differential biases the sheets toward each other so that their spacing is maintained by the spacer means. The upper sheet which is exposed to solar energy may be thin, and the sheets are free to move away from each other at the location of the spacer means so that permanent damage will not result when the heat exchange liquid expands by freezing or when there is excessive flow of liquid through the flow passage in the absorber panel.

I claim: 
     
       1. A solar collector system comprising a plurality of absorber panels for receiving radiant solar energy, each of said absorber panels having an internal flow passage,   a circulatory system including means entirely filling said passages with heat-receiving liquid and circulating said liquid through said absorber panels, said circulatory system including an inlet manifold line connected by inlet branch lines to a plurality of said absorber panels and an outlet manifold line connected by outlet branch lines to a plurality of said absorber panels, pressure reducing means in a plurality of said branch lines to provide said absorber panels with absolute pressure which increases progressively in a direction which is downstream with respect to the associated manifold line, said circulatory system including means for maintaining said absolute pressure at subatmospheric pressure.   
     
     
       2. The solar collector of claim 1 wherein said pressure reducing means are in said inlet branch lines. 
     
     
       3. The solar collector of claim 1 wherein said pressure reducing means are bodies providing orifices of different sizes. 
     
     
       4. The solar collector of claim 3 wherein said pressure reducing means are in said inlet branch lines. 
     
     
       5. The solar collector of claim 1 wherein each of the absorber panels is formed of a pair of substantially parallel sheets which have interior and exterior surfaces, said interior surfaces facing each other and being spaced apart to provide therebetween a flow passage space, and spacer means for limiting the movement of said sheets toward each other whereby the subatmospheric pressure biases the sheets toward each other and the thickness of the flow passage space is established by the spacer means.   
     
     
       6. The solar collector of claim 5 wherein the plates are inclined from the horizontal to produce elevation differences along the flow passage, said means for supplying liquid causing liquid to flow downwardly in the flow passage to produce hydrodynamic losses which maintain a pressure which is substantially constant along the length of the flow passage. 
     
     
       7. The solar collector of claim 5 wherein said spacer means are integral with one of said sheets. 
     
     
       8. The solar collector of claim 7 wherein said projections are dimples spaced apart by a distance of about 3/8 inch to about 1/2 inch. 
     
     
       9. The solar collector system of claim 5 wherein the flow passage space has a size providing hydrodynamic losses in a liquid moving therethrough, said sheets being inclined from the horizontal to provide elevation changes along the flow passage space, said inlet branch lines being connected to said absorber panels at higher elevations than the corresponding said outlet branch lines causing liquid to flow downwardly through said absorber panels, whereby said hydrodynamic losses have an opposite effect on pressure than said elevation changes to reduce pressure differences along the length of the flow passage.